Accurate measurement of throttle position is important when using engine control means for automotive applications. Past designs of throttle position indicators include two-position throttle switches and various potentiometric devices.
The two-position throttle switch provides an electrical signal to the engine control means when the throttle is in one of two positions: typically closed and wide open. These switches require service after a period of use as exposure to an automotive environment may cause the deterioration of the materials in the switch. Service or replacement of the switch would eventually be necessary in order to provide the electronic engine controls with an accurate indication of the throttle position.
Another throttle position indicator which has been used is a potentiometric device. This is also known as a throttle pot. The throttle pots are mounted on the exterior of the throttle body or carburetor and are connected to the throttle blade linkage in such a fashion so as to deflect the wiper arm of the throttle pot in proportion to the movement of the throttle blade. The potentiometric location of the closed throttle position and the wide open throttle position is established during the assembly process. This is done by mechanically mounting the throttle pot with the wiper arm in a pre-established location with respect to the fully closed position of the throttle blade. The throttle pot then provides readings to the engine control means, all referenced to the mechanically set base line, which is usually the closed throttle position. The accuracy of the adjustable throttle pot is in direct proportion to the skill of the assembler and to the integrity of the mechanical fastening means holding the throttle pot to the throttle body. Eventually, the adjustable throttle pot may need service to account for wear in the throttle blade linkage and possible deterioration of the potentiometer.
The subject invention seeks to eliminate the need for mechanical adjustment of the throttle pot during the assembly process and also seeks to eliminate the need for service adjustments on the adjustable throttle pot due to throttle body linkage wear.
This is accomplished by using a conventional throttle potentiometer with a modified mounting mechanism which is nonadjustable. In other words, the assembler will need only to affix the throttle pot to the throttle body at the designated location and insert the appropriate mounting devices, such as screws, through fixed guiding means. The assembly can then be completed without the need of any adjustments or decisions to be made by the assembler.
The need for an accurate measure of the throttle position still exists so the engine control means is now employed: to continuously check the position of the throttle, to memorize the lowest throttle position reading from the throttle pot, and to define this position as closed throttle. The reading is then updated to compensate for wear in the throttle blade linkages or in the potentiometric device or due to temperature or other conditions. The engine control means will read and retain the lowest measured value of the potentiometric voltage output. This value will then be stored in memory and identified as the closed throttle output until it is necessary to redefine it.
Additional features of measuring the throttle position in the above-described manner include: the prohibition of false readings due to low cranking voltages; the establishment of a default value upon the reset of memory (usually due to the disconnection of the battery); the ability to reset (a default condition) if no closed throttle indication occurs between two sequential cranking events.